Phosphate flotation process



Aug. 19, 1969 c. H. cs. BUSHELL ETAL 3,462,016

I PHOSPHATE FLOTATION PROCESS Filed Aug. 28, 1967 PHOSPHATE ROQK 10 d CRUSHER kffimvmm' r FINE GRND OVERSIZE 39A$Q9$ CLASSIFIERS COLLECTOR 5 ALKAU CONDITIONER OVERFLOW gg rsr STAGE Fm I FLOTAT/ON 22 UNDERFLOW THICKENERSJ/ A Qf TH/CKENER PHOSPHOR/C f ACID CONDITIONER ANION/C .UNDERFLOW, FLOTAT/ON REJECTS. coLLEcroR 2s Y 2ND STAGE FLOTAT/ON OVERFLOW, RECYCLE 0R SOLUTION WASTE FLOAT ovERFLow REcvc/ E 0R 32 WASTE UNDERFLOW 2e OVER- THICKENER TH/CKENER FLOW I UNDERFLOW FILTER 7 I F/LTRATE UNDERFLOW REJECTS PHOSPHATE CONCENTRA rs 1-\ v1;1\/'r01a.

a xmis Agent United States Patent 3,462,016 PHOSPHATE FLOTATION PROCESS Charles Herbert George Bushell, Montrose, British Columbia, Horst Eberhard Hirsch, Trail, British Columbia, and Randolph Mathias Lauer, Chapman Camp, British Columbia, Canada, assignors to Cominco Ltd., Montreal, Quebec, Canada, acompany of Canada Filed Aug. 28, 1967, Ser. No. 663,640

Claims priority, application Canada, Dec. 29, 1966,

Int. Cl. B03d 1/00 US. Cl. 209-166 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for beneficiating phosphate-bearing materials and is particularly directed to an improved process for separating calcium and magnesium carbonates from phosphate minerals.

It is known to upgrade phosphate values in a phosphatecontaining ore by means of flotation. One generally accepted process comprises suspending finely ground phosphate rock in a slightly alkaline aqueous solution containing a carboxylic acid or other anionic flotation reagent and subjecting the suspension to a first froth flotation step in which the phosphate values are concentrated and collected in the froth and a substantial portion of the siliceous gangue material is depressed and separated as the underflow tailing product. The concentrate from this first flotation step is then treated with sulphuric acid to remove the negative-ion collector reagent, filtered and washed with water to remove the residual sulphuric acid. The concentrate is then suspended in a neutral or substantially neutral aqueous solution containing an amine or other cationic flotation reagent and subjected to a froth flotation step in which the residual silica is collected in the froth and an enriched phosphate-containing concentrate is recovered as the underflow product.

A disadvantage of this process is the necessity for maintaining two separate and distinct flotation circuits, the first anionic and the second cationic, with the attendant problem of removing the flotation reagents from the concentrate from the anionic circuit before commencing treatment in the cationic circuit:

Another known process is that disclosed in US. Patent No. 3,113,838 issued Dec. 10, 1963. This patent describes a flotation process which employs a fatty acid in the presence of soluble alkaline phosphate produced by dissolving phosphate salt or by attacking a portion of the phosphate rock with a mineral acid such as sulphuric acid until phosphoric acid is freed, to transform calcium phosphate into a soluble phosphate. This acid addition is impractical when treating phosphate rock containing substantial amounts of silica as well as calcium and magnesium carbonates. In the presence of soluble phosphates there is no effective separation of phosphate minerals from silica and silicates.

Also, the treatment of a carbonate containing ore with a strong mineral acid, such as sulphuric acid, would require the addition of an excessive amount of acid due to the preferential attack on the carbonates, and would unfavorably alter the characteristics of the feed to the flotation operation.

It is important for the production of a phosphate concentrate suitable for use in the Wet phosphoric acid process that carbonate containing minerals, especially magnesium-containing carbonates, be maintained at a minimum. The presence of carbonates not only causes undesirable foaming in the reactor chambers and undue consumption of acids, but also the magnesium content in the carbonates forms a magnesium sulphate which is soluble in phosphoric acid producing a magnesium salt upon subsequent ammoniation of the phosphoric acid which lowers the value of the ammonium phosphate fertilizer product. Also, the presence of magnesium in the phosphoric acid raises the viscosity of the salt.

We have discovered that a phosphate concentrate produced from a conventional first stage anionic flotation circuit which has been conditioned in the presence of a small amount of phosphoric acid in an aqueous solution to produce a pH of from 4.5 to 5.8 can be passed to a second stage anionic flotation circuit, with or without additional amounts of the same flotation reagents as those used in the first stage, to provide an effective separation and removal of the phosphate minerals from the nonphosphate gangue minerals, especially the deleterious calcium and magnesium carbonate minerals.

It is a principal object of the present invention, therefore, to provide a twostage anionic flotation circuit for beneficiating phosphate-bearing materials which obviates the necessity of neutralizing or destroying the flotation reagents used in a first stage anionic flotation circuit prior to reflotation treatment of the concentrate from the first stage.

Another object of the present invention is the removal of a major portion of residual calcium and magnesium carbonate minerals present in a phosphate mineral concentrate made from a siliceous ore.

And another object of the invention is the provision of a process which permits utilization, and recovery for re-use, of an inexpensive conditioning agent.

These and other objects of the invention and the manner in which they can be attained will become apparent from the following description of the process as illustrated in the drawing in which:

The drawing provides a schematic illustration of a flowsheet showing the process steps of an embodiment of the invention.

According to the process of the invention, the phosphate rock to be beneficiated preferably is subjected, after appropriate comminution, to a primary anionic flotation stage, using fatty acid collector reagents such as oleic acid, stearic acid, or other carboxylic acids, including tall oils and the like, to provide an enriched phosphate concentrate containing calcium and magnesium carbonates as a froth product and a silica tailing as an unde'rflow depressed product. Phosphate rocks, containing such minerals as cellophane, are first comminuted for liberation of the phosphate minerals from the gangue minerals. The degree of grinding applied to the rock will depend, of course, on the texture of the rock and association of the phosphate values with the gangue minerals.

With reference to the flowsheet of the drawing, it will be seen that the phosphate rock is comminuted to the desired size range necessary to liberate the phosphate values from the gangue by crushing and grinding steps 10 and 12 respectively and classified in classifiers 14 to yield a sized product which is suspended in Water or recycled solution and conditioned in stage 16 by the addition of carboxylic acid, sodium silicate and an alkali for a pH of 9 to 10.5. The conditioned material is subjected to a first stage flotation 18 in an anionic circuit for production of a phosphate-enriched float concentrate and a siliceous gangue underflow. The gangue normally is thickened in stage 20 and discharged to waste. The primary separation of phosphate minerals from siliceous gangue minerals as described above is well known in the art.

The phosphate-enriched float concentrate is then thickened in a thickener or hydroclone stage 22 and passed to a conditioner 24 having an aqueous solution therein maintained at a pH in the range of from about 4.5 to 5.8 by the controlled addition of phosphoric acid. The conditioned slurry, to which is added carboxylic acid, is then passed to a second stage anionic flotation circuit 26 for production of an overflow product of gangue material, especially calcium and magnesium carbonate minerals, and an underflow product of phosphate-enriched concentrate which is thickened in stage 28 and the thickener underflow filtered in unit 30 for the production of a phosphate concentrate. The float product from the flota- The concentrate from the first stage separation was pumped to a thickener and the thickener underflow containing approximately 65% solids was pumped to a conditioning tank and the following reagents were added:

Phosphoric acid, (H PO 3-8 lbs. per ton of first stage concentrate to produce pH 4.5 to 5.8 when diluted as described below.

Tall oil (fatty acid), 0 to 3 lbs. per ton of first stage concentrate This suspension was then diluted with water to contain 3-0 to solids by Weight and fed to a flotation machine.

Table 1 below gives the analysis, weight and percent distribution of the P 0 CaO, MgO and SiO contained in the feed, concentrate and tailing produced in the first stage separation.

Table 2 gives the analysis, weight and percent distribution of the P 0 CaO, MgO and SiO contained in the concentrate and tailing produced in the second stage separation.

Table 3 provides a comparison of the first stage recoveries relative to the overall recoveries of the process.

TABLE 1.FIRST STAGE SEPARATION Distribution (percent) MgO CO2 SiOz Wt. P205 C80 MgO CO2 S102 Feed 20. 2 3 5 0. 9 3. 5 28. 5 Concentrate (overflow) 30. 6 45. 1 1. 17 5. 3 10. 5 2 8 8 2 3 Zi Z Tallings (underfiow) 5. 8 12. 7 0. 53 1. 0 53. 4 42 12. 1 17.0 24. 6 12: 2 78: 6

TABLE 2.SECOND STAGE SEPARATION Composition (percent) Distribution (percent) P205 CaO MgO C02 810; Wt. P205 (3210 MgO CO2 sio Feed 30.6 45.1 1.17 5.3 1 Concentrate (underflow)--. 32. 1 46. 1 0. 50 3 7 10.? g 8 35 8 65 9% Tailings (overflow) 15.8 35.2 7.78 21.1 8.5 9.2 4.8 7.2 61:2 36:6 715 tion circuit 26 normally is also thickened in unit 32 and the thickener underflow discharged to waste. The solutions 40 recovered from units 28, 30 and 32 can be discharged to TABLE 3- RECOVERIES (PERCENT) waste or re-cycled to conditioner 24 for utilization of the P205 CaO MgO Go, Slog reagents therein. First 8m 83 0 It will be understood that the addition of flotation re- Overall 83.7 7710 531% 2%? iii: agents such as carboxylic acid and the like may not be necessary due to the presence of flotation reagents retained from the first stage anionic circuit. The rate of addition It b of phosphoric acid for conditioning the feed to the second h W1 6 noted r the above tables that 95.2% of stage is primarily determined by the pH of the aqueous e P205 cohtalhed the feed the l ld stage flotasolution. We have found that optimum results are atnon Was recovered 1n the flotatlon machine underflow tained with a pH Within the range of from about 4.5 to and that 611% of the Mgo Was rejected n the v ra'bout 5.8. With diiferent ores, however, this optimum the Overall recovery of 2 5 being 837% and t H range may vary somewhat, for example, from about overall recovery of MgO being 29.3%. The effective pH 4 to about pH 6. The eflectiveness of the separation reduction of MgO in the concentrate relative to the feed of calcium and magnesium carbonates from the phoswas therefore (100-29.3)=70.7%. phates in the second stage anionic flotation circuit is reduced with solution pHs outside this range of about EXAMPLE 2 4 to 6.

The followi g eXamples Show the efieehvehess of the In this example of the process an ore comminuted as present process 1n the treatment of a collophane phosphate rock indigenous to the Western United States.

EXAMPLE 1 Lbs. per ton of ore Fatty acid 1.5 Sodium hydroxide 3.0 Sodium silicate 1.0

The liquid-solids ratio of this suspension was adjusted to 30 to 35% solids by weight and the suspension was fed to a flotation machine.

described above was treated according to the conditions set forth in Example 1.

Tables 4, 5 and 6 below provide data for the first stage separation, second stage separation and recoveries of the first stage relative to the first and second stages combined respectively, as was described hereinabove with reference to Tables 1, 2 and 3. It will be noted that 94.7% of the P 0 contained in the feed to the second stage flotation was recovered in the flotation machine underflow and that 67.1% of the MgO was rejected in the overflow; the overall recovery of P 0 being 80.3% and the overall recovery of the MgO being 27.0%. The effective reduction of MgO in the concentrate relative to the feed was therefore (27)=73.0%.

Composition (percent) Distribution (percent) P205 0110 MgO col S101 wt. P205 0110 MgO C02 5101 Feed 19. s 30.8 1. 1 a. 7 29. 1 100 100 100 100 100 100 Concentrate (overflow) 30. 45. O 1. 63 6. 0 10. 56 84. 8 81.8 83. 0 90. 8 20. 2 Tailings (underflow) 6. s 12. 7 0. 43 0.8 52. s 44 15. 2 18. 2 17. 0 9. 2 79. 8

TABLE 5.SECOND STAGE SEPARATION Composition (percent) Distribution (percent) P205 CaO MgO CO2 S102 Wt. P105 0110 MgO C01 SiOz Feed 30. o 45. 0 1. 63 G. 0 10. 5 100 100 100 100 100 100 Concentrate (underflow)--. 32. 1 45. 6 0. 60 3. 6 10. 5 88. 6 94. 7 89. 8 32. 5 52. 9 89. 4 Tailings (overflow) 13. 7 40. 4 9. 63 24. 6 9. 7 11. 4 5. a 10.2 67. 5 47. 1 10. 6

TABLE srREoovEmEs (PERCENT) What we claim as new and desire to protect by Letters P O C O M O 00 so Patent of the United States is:

a g 1 1. A process for beneficiating a siliceous phosphate lgirst s t age recoyeries 3 1 83%.? @2-3 3%? 2%? rock high in calcium carbonate and magnesium carbonvem ewvmes ate comminuted for the substantial liberation of phos- Although it will be understood that the present invention is free from hypothetical considerations, it is believed that the improvement in the present process, the separation of a major portion of the residual calcium and magnesium carbonates from the phosphate concentrates in the second stage of a two-stage anionic circuit, results from the addition of a small amount of phosphoric acid to the feed for the second stage. It is not definitely ascertained why the addition of phosphoric acid to the feed to the second stage should result in the depression of the phosphate particles and the flotation of the residual gangue material, which is contrary to what occurs in the first stage separation in which the phosphate particles float and the silica gangue is depressed. The lowering of the pH by the addition of sulphuric acid or other acids is not sufficient, per se, in bringing about the improvement of the present invention. It appears that the presence of a phosphate ion may be instrumental in aflecting the flotation characteristics of the phosphate mineral possibly because of its eflect on the solubility relationships of the phosphate particles and gangue particles in the suspension.

The present invention provides a number of important advantages. Phosphate-bearing materials can be beneficiated by the removal of gangue materials such as calcium and magnesium carbonates in a two-stage anionic flotation circuit by the simple expedient of adding phosphoric acid, a product from the wet phosphoric acid process to which the phosphate concentrate is subsequently subjected, to the concentrate from the first stage flotation. The reagents from the first stage need not be destroyed and can often provide the necessary concentration of reagents to effect the subsequent flotation operation in the second stage.

phate values from silica, calcium carbonate and magnesium carbonate by froth flotation which comprises the steps of subjecting said phosphate rock in finely-divided form to a primary anionic flotation, separately withdrawing from said primary flotation an underflow tailings product high in silica content and a phosphate-enriched float product containing calcium carbonate and magnesium carbonate, conditioning said phosphate-enriched float product in an aqueous solution having phosphoric acid added thereto in amount suificient to maintain a pH within the range of from about 4.5 to about 5.8, subjecting said conditioned float product to a secondary anionic. flotation and separately withdrawing from said secondary flotation a float product high in calcium carbonate and magnesium carbonate and an underflow concentrate product high in phosphate-bearing minerals.

2. In a process as claimed in claim 1, recovering the aqueous solution having phosphoric acid added thereto and recycling said solution to the conditioning step.

References Cited UNITED STATES PATENTS 2,442,455 6/1948 Booth 209166 3,032,197 5/1962 Northcott 209-166 3,113,838 12/1963 Perri 209166 X 3,259,242 7/1966 Snow 209-166 FOREIGN PATENTS 468,161 9/ 1950 Canada.

HARRY B. THORNTON, Primary Examiner R. HALPER, Assistant Examiner 

